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Chrysanthemum White Rust by Jane Trolinger, Ph.D. Syngenta Flowers, Inc. Today’s Topics CWR caused by Puccinia horiana How Chrysanthemum White Rust (CWR) can impact chrysanthemum production How to recognize the

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chrysanthemum white rust

by Jane Trolinger, Ph.D.

Syngenta Flowers, Inc.

today s topics
Today’s Topics
  • CWR caused by Puccinia horiana

How Chrysanthemum White Rust

(CWR) can impact chrysanthemum


How to recognize the


How to protect your crops

importance of chrysanthemum white rust caused by puccinia horiana
Importance of Chrysanthemum White Rust caused by Puccinia horiana

Can spread rapidly in a greenhouse or nursery resulting in severe losses

A quarantine disease in the United States and Canada

Introduction from overseas has had a significant impact to the chrysanthemum industry in US and Canada



New observation in 2010:

Pustules can also be found

on the upper leaf surface


Another new observation in 2010:

Purple rather than yellow spots associated

with the white pustules


Note yellow spots and pustules

on upper leaf surface

brown rust or chrysanthemum rust is distinct from cwr
Brown Rust or Chrysanthemum Rust is distinct from CWR
  • Puccinia tanaceti (Puccinia chrysanthemi)
  • Chocolate brown pustules
  • Present in U.S.
  • Rarely causes heavy losses
  • Not a quarantine pest
do not confuse white or brown rust with slime mold
Do not confuse White or Brown Rust with Slime Mold

Close up

Slime Mold on underside chrysanthemum leaf

with most fruiting bodies erupted

Slime Mold on underside of

chrysanthemum leaf

Slime Molds do not infect plants but they blemish them

by growing on the surface of plants

chrysanthemum white rust pustules
Chrysanthemum White Rust Pustules

Most common on young leaves and flower bracts

Can be found on any green tissue; this is a way CWR can move on cut flowers


cwr host range 12 species of chrysanthemum susceptible
CWRHost Range 12 species of chrysanthemum susceptible
  • Pot mums, cut mums, and garden mumsChrysanthemum morifolium
  • Nippon daisy or Montauk daisy Nipponanthemum nipponicum
  • Ajania pacifica(syn.Chrysanthemum pacificum)
  • Giant daisy or High daisy Leucanthemella serotina, (syn. Chrysanthemum serotinum)

Click here for USDA Host Range (Appendix VI)(See page 19)

Note: When opening links from this Webinar, close the link after viewing -- and before you try to open the next link!

how does cwr infect mums

Spores are carried through the air, by humans, or by water from an infected plant to a new plant

Two kinds of spores:

Surviving spores (teliospores)

Infecting spores (basidiospores)

Why is that important?

The 2nd spore type (basidiospore) must be formed before there will be any appreciable spread of the disease and conditions must be correct before the 2nd spore type is formed at all

the survivors teliospores
The survivors - teliospores

Can last for 8 weeks on dried leaves! They survive only one to three weeks if infected tissue is buried under soil – so bury your cull piles with at least 2 inches of soil!

Are produced in pustules and remain in pustules unless the teliospores are aggressively brushed off

Produce the basidiospores when conditions are moist for 3 hours (optimum temperature = 63°F)

the infectors basidiospores
The “infectors” - basidiospores

Can cause epidemic if conditions are right

Spread from plant to plant by splashing water and human handling

Must have film of water on plant surface for infection

Infection (host penetration) can occur in 2 hours at optimum temperature of 63°F

Can travel up to about 1/2 mile by wind currents during moist weather


--only 5 minutes when relative humidity is 80% or below

--and less than 60 minutes when relative humidity is 90%

possible sources of cwr for us and canada
Possible sources of CWR for US and Canada

Imported chrysanthemum cut flowers with infection

Smuggled chrysanthemum material

Overwintering (?) in environment

(currently being researched)

how do we try to keep white rust out of the us and canada
How do we try to keep white rust out of the US and Canada?

White rust prevention system required by USDA in countries exporting cut mums to U.S.

Inspection of chrysanthemum cut flowers at U.S. ports of entry (note: no inspection in Canada)

Quarantine of imported propagation material (cuttings) into U.S.

Click here for more details

cwr prevention within the us and canada
CWR Prevention within the US and Canada

Plant ONLY cuttings from reputable commercial source

Scout crop regularly from stick to sale

Imported cut mums should never be handled in or near mum-growing facilities because spores can be moved by worker handling and by wind (up to ½ mile away)

-They can be infectedand not yet show symptoms or signs

Maintain low humidity and dry foliage

Schedule regular applications of preventive fungicides if you are in an area where CWR has been previously reported e.g. if within ½ mile of residential area or cemetery

fungicides useful to prevent cwr alphabetized by brand
Fungicides useful to prevent CWR (alphabetized by brand)

Banner Maxx® (propiconazole)

Cygnus® (kresoxim-methyl)

Daconil Ultrex® (chlorothalonil)

Dithane® 75 DF (mancozeb)

Heritage® (azoxystrobin)

Insignia® (pyraclostrobin)

Pageant® (pyraclostrobin + boscalid)

Strike® (triadimefon)

Terraguard® (triflumizole)

Eagle® (myclobutanil) is best used as an eradicant and not as a preventive. If you are in a high risk area and conditions are favorable for CWR, we recommend a prevention program (described in CWR Bulletin).

©2010 Syngenta Flowers, Inc., P.O. Box 1349, Gilroy, California 95021. Important: Always read and follow label instructions before buying or using Syngenta products. The instructions contain important conditions of sale, including limitations of warranty and remedy. Banner Max®, Daconil Ultrex®, Heritage®, and the Syngenta logo are registered trademarks of a Syngenta Group Company. Dithane®. Pageant® and Eagle® are registered trademarks of Dow AgroSciences, LLC.  Cygnus® is a registered trademark of BASF Corporation. Strike® is a registered trademark of OHP, Inc.  Terraguard® is a registered trademark of Chemtura Corporation.

Click here for spray schedule(See page 4)

if you find cwr
If you find CWR

Report it: this is the law

S. Anwar Rizvi USDA-APHIS-PPQ-EDP,  Unit 160 4700 River Road, Riverdale, MD  20737 Tel: (301) 734-4313 E-mail:

Inform USDA, CFIA, state, or county regulatory officials

Regulatory officials will supervise eradication and treatment program

why is it important to report chrysanthemum white rust
Why is it important to report chrysanthemum white rust?

Make sure grower and retailer losses are minimized

Try to keep it from spreading in the chrysanthemum industry

Collect data on the location of the finds and document information about the disease spread to maximize prevention for the future

eradication and treatment program
Eradication and treatment program

Infected nursery (chrysanthemums) will receive an Emergency Action Notice preventing shipment until declared “free”

Required destruction of symptomatic plants and the surrounding one-meter radius

Three treatments, at 5-7 day intervals, with eradicant fungicide (e.g. myclobutanil = Eagle)

Final inspection 5-7 days after 3rd treatment; if no CWR, plants released for sale

Can be very disruptive to normal business operations

click here for US National Protocol

you and your inspector
You and Your Inspector
  • Become familiar with the National Protocol for CWR eradication by visiting
  • Be aware that if a “stop shipment” has been placed on your crop and the inspections are being prolonged while CWR might be spreading, you may have the right to ask that the inspections be done in sections.
  • This may then enable you to go ahead and begin the eradicant fungicide applications in completed areas thereby better protecting your yield.
in conclusion
In Conclusion
  • Click Here for CWR Bulletin
photo credits
Photo credits

2, 4, 5, 6, 7 Pennsylvania Dept of Agriculture and USDA, APHIS (permission Anwar Rizvi)

8, 12 Margery Daughtrey, Cornell University

13a Mark Esoldo, Syngenta Flowers, Inc.

9, 10, 11 Tracey Olson, Pennsylvania Dept of Agriculture